The present invention relates to an electric power generator including a hydrogen generator and a polymer electrolyte fuel cell. More specifically, the present invention relates to an electric power generator, which uses a residual fuel gas exhausted from a fuel electrode of the fuel cell and/or an incompletely generated gas exhausted from the hydrogen generator not having a desired composition as a part of a burning fuel gas for heating the hydrogen generator.
(1) Electric Power Generator
A conventional electric power generator using a polymer electrolyte fuel cell will be described with reference to FIG. 3. In a polymer electrolyte fuel cell 1, an air electrode 2 and a fuel electrode 3 are disposed so that they sandwich a polymer electrolyte membrane 9 (for example, Nafion 117 manufactured by Du Pont). To the upstream side of the air electrode 2, a fan 4 for supplying the air is connected, and to the upstream side of the fuel electrode 3, a hydrogen generator 6 is connected via a switching valve 5. A burner 7 is provided adjacent to the hydrogen generator 6 and the hydrogen generator 6 is heated with heat generated in the burner 7. In the upstream side of the burner 7, a burning fuel flow rate controlling valve 8 is disposed.
When a raw material fuel such as natural gas or methanol and a raw material water necessary for the steam reforming reaction are supplied to the hydrogen generator 6 and a burning fuel is supplied to the burner 7 via the burning flow rate controlling valve 8, the temperature of the hydrogen generator 6 is increased to a predetermined temperature with a burning heat generated in the burner 7. Hydrogen gas generated in the hydrogen generator 6 is not necessarily a pure hydrogen gas and may contain impurity gases such as carbon monoxide and carbon dioxide, and therefore it is sometimes called hydrogen rich gas. In a gas generated when the temperature of the hydrogen generator 6 is outside the predetermined temperature range, a large amount of poisoning components such as CO is contained, and this gas is exhausted from the hydrogen generator 6 as an incompletely generated hydrogen rich gas which does not have a desired composition. This incompletely generated gas is not supplied to the fuel electrode 3 but exhausted to the outside via the switching valve 5.
When the temperature of the hydrogen generator 6 is increased to a predetermined temperature and a hydrogen rich gas having a desired composition is obtained, this is supplied to the fuel electrode 3 by operating the switching valve 5. Then, the polymer electrolyte fuel cell 1 starts electric power generation. Most of the hydrogen in the hydrogen rich gas supplied to the fuel electrode 3 is consumed in the electric power generation and the gas containing residual hydrogen is exhausted outside as a residual fuel gas from the fuel electrode 3.
In this manner, in the conventional electric power generator using a polymer electrolyte fuel cell, when the temperature of the hydrogen generator 6 is not in the predetermined temperature range, a large proportion of impurity gas other than hydrogen is contained in the generated gas, so this cannot be used as a fuel for the fuel electrode and is exhausted outside as an incompletely generated gas. As a consequence, there has been the problem that this incompletely generated gas might possibly catch fire with some fire source.
Further, the residual fuel gas exhausted from the fuel electrode 3 contains hydrogen that has not been consumed in the electric power generation. Consequently, the residual gas may also possibly catch fire with some fire source. Moreover, even if the residual fuel gas does not catch fire, there has been the problem that the operation efficiency of the electric power generator is decreased since a part of the hydrogen generated in the hydrogen generator is exhausted outside.
In this regard, the present invention has an object (first object) to solve the above-described problems that the prior art presents and to provide an electric power generator which does not exhaust outside the off gas containing hydrogen as it is, which does not have any possibility of inappropriately catching fire, and which have a high operation efficiency.
On the other hand, the hydrogen generator used in the electric power generator as above generates hydrogen using hydrocarbons such as natural gas, LPG, gasoline, naphtha, kerosene and methanol, water and the air. This is because hydrogen attracts attention as a prospective energy source substituting for fossil fuels.
In order to utilize hydrogen effectively, it is necessary to provide infrastructure such as hydrogen pipelines. As a method for providing such facilities, it is studied to use infrastructure which has already been built for transportation and conveyance of fossil fuels such as natural gas and fuels such as alcohol, and to reform the above fuels to generate hydrogen in the place where hydrogen is needed. For example, there have been a variety of propositions with regard to on-site electric power generator of medium and small size, namely, a technique of reforming natural gas (city gas) for fuel cells and a technique of reforming methanol for fuel cells as a power source for automobiles.
In order to reform the above fuels to generate hydrogen, a catalytic reaction at a high temperature is used, and typically, a steam reforming method, and an auto-thermal method using both a steam reforming and a partial oxidation together are used.
However, since a reforming reaction proceeds at a high temperature, an obtained reformed gas contains not only hydrogen but also carbon monoxide (CO) and carbon dioxide (CO2) as by-products through reaction equilibrium. When the reformed gas is used in a fuel cell, particularly in a polymer electrolyte fuel cell, CO as a by-product poisons electrodes of the fuel cell and significantly deteriorate the performance thereof. For this reason, it is necessary to reduce the concentration of CO and CO2 in the reformed gas to the lowest possible. For this purpose, in general, a modifying reactor for shift-react CO and water, and a CO purifier using CO oxidation method or methanation method are equipped downstream side of the reforming reactor to reduce the CO concentration in the reformed gas as low as several tens of ppm. Although the CO concentration of the reformed gas is around 10%, the CO concentration of a modified gas obtained after the reformed gas passes through the shifter is reduced to around 1%. Further, the CO concentration of a purified gas obtained after the modified gas passes though the CO purifier is reduced to several tens of ppm and this is supplied to the fuel cell.
Herein, specific catalytic temperatures in the reforming reaction, modifying (shift) reaction and CO purifying reaction are 650 to 750xc2x0 C., 200 to 350xc2x0 C. and 100 to 200xc2x0 C., respectively. In particular, if the temperature of the purifier does not reach the temperature range, the CO concentration cannot be reduced to several tens of ppm and the obtained purified gas cannot be supplied to the fuel cell. As a consequence, the starting time of the fuel cell depends on the start-up time of the catalytic temperature of the purifier. Also, the temperature of the modifying catalyst contained in the shifter reaches the active temperature with waste heat after the termination of the reforming reaction, and the modifying reaction starts. Moreover, the temperature of the purifying catalyst contained in the CO purifier reaches the active temperature with waste heat after the termination of the modifying reaction, and the modifying reaction starts.
However, in some operation method, condensed water generated in the reaction in the reformer, shifter and purifier stays inside the gas pathway and this may delay the start-up time before the respective catalytic temperatures reach the predetermined temperatures. For example, when the operation is stopped after a short time has passed from the start of operation of the hydrogen generator, the temperature of the shifter and the purifier is not sufficiently increased, and water content in the reformed gas from the reformer and the modified gas from the shifter may condense and collect as condensed water in the lower portion of the purifier. When the hydrogen generator starts operation again under such condition, there is the problem that, since extra heat is needed to vaporize the collected condensed water, it takes a long time to increase the temperature of the purifying catalyst to the active temperature.
In view of this, with regard to the hydrogen generator used in the electric power generator, the present invention has an object to shorten the time before the temperature of the catalyst in the purifier reaches the catalytic active temperature (second object).
Next, as described above, in each of the reformer, shifter and purifier inside the hydrogen generator, a catalyst corresponding to the respective reaction is disposed. Since the reaction temperature varies in each catalyst, the temperature of each catalyst is required to be heated to the respective active temperature in order to generate and supply hydrogen stably. The reaction temperature of the reformer positioned upstream in the flow of the raw material fuel and several gases is the highest and the reaction temperature of the purifier is the lowest. For this reason, in the hydrogen generator using the conventional steam reforming method, the shifter and the purifier are heated successively with heat from the reformer (for example, heat retained in the reformed gas) or excess heat from the burner disposed in the reformer, in some cases.
As a consequence, in the case where the temperature of the respective reformer, shifter and purifier is not appropriate, hydrogen generation does not proceed effectively. For example, in the steam reforming method, water is supplied so as not to be short of stoichiometric amount of oxygen atoms necessary for generation of carbon dioxide from reaction of carbon atoms in the raw material fuel. Also, in order that the raw material fuel reacts with water, it is necessary that water is at least present in the form of steam.
However, in the case where the temperature of the reformer is low, the reforming reaction does not proceed even if water is supplied and water stays inside the hydrogen generator. Also, if the raw material fuel and water are supplied after the temperature of the reformer is increased, there is the possibility that the catalyst is deteriorated with heat in the heating process and the catalytic activity is decreased. For this reason, it is necessary to supply the raw material fuel and water while setting at an appropriate temperature. Further, the temperature of the gases in the downstream side from the reformer becomes higher than the heat-resistant temperature of the modifying catalyst. Consequently, in the case where gases having temperature over the heat-resistant temperature flow, it is necessary to actively cool from the reformer to the shifter to prevent the catalyst from deteriorating and losing the catalytic activity thereof.
Also, it is an object of the hydrogen generator to reduce sufficiently the CO concentration of the modified gas in the purifier and to supply the obtained purified gas as a hydrogen rich gas. However, it is complicated to measure the CO concentration at every start of the hydrogen generator and judge the time to start the supply of hydrogen according to the concentration. For this reason, desired is a simple and accurate method for detecting that the hydrogen generator in the electric power generator is in the normal operation condition (third object).
As the above-mentioned reforming catalyst, to be specific, a base metal such as nickel or a noble metal such as ruthenium is used, and as a modifying catalyst, a base metal of copper base or a noble metal such as platinum is used. Also, as the CO removing (purifying) catalyst, a noble metal such as platinum is used. In order to make sure that the reaction progresses in the respective reactors (reformer, shifter or purifier), it is necessary to strictly control the temperature of the above catalysts in a constant range.
If the catalytic activity is in a satisfactory condition, the reaction taking place in the reformer and the shifter is the equilibrium reaction, and the composition of the obtained gas can be determined unambiguously only by controlling the temperature under a constant pressure condition. This results from the fact that the reaction in the CO purifier is a reaction including disturbing factors of equilibrium reaction. As a consequence, in order to operate stably the hydrogen generator in the stationary state generating a constant amount of hydrogen or in the transient state where the amount of generated hydrogen varies, and to obtain a generated gas of a constant composition including by-products, it is the most important to maintain the temperature of the respective reactors as constantly as possible. In particular, if the generation amount of the generated gas is changed, the temperature of the respective reactors is liable to change, and therefore there is the problem that it is difficult to largely change the generation amount thereof.
In this regard, the present invention has an object to propose temperature detecting sites of the respective reactors and specific methods of temperature control corresponding thereto, thereby to provide a hydrogen generator excellent in operation property and convenience (fourth object).
Incidentally, known as dispersed type electric power generators are gas turbines and engines that generate electric power using burning energy of the fuel, and fuel cells using chemical reactions. Since fuel cells do not include physical operative part and are high in power generation efficiency, they attract attention from the viewpoint of energy saving. Most of the fuel cells generate electric power using hydrogen as the fuel. However, since infrastructure for hydrogen has not been established at the present time, hydrogen is generated by reforming hydrocarbon gases or raw materials such as naphtha and this hydrogen is supplied.
For example, phosphoric acid type fuel cells have been systemized using a hydrogen generator that generates hydrogen by steam reforming city gas and have been put into practice as stationary electric power generators. Also, polymer electrolyte fuels cells have been systemized with a hydrogen generator that reforms alcohol or city gas, and they are now being applied to electric power generator for automobile and home.
In these fuel cells, the amount of consumed hydrogen varies according to the amount of electric power. When the amount of electric power is changed, it is necessary to change the amount of hydrogen supplied from the hydrogen generator accordingly. However, if the amount of generated hydrogen is suddenly change, the temperature balance in the hydrogen generator is lost and hydrogen cannot be generated steadily. For this reason, the phosphoric acid type fuel cell power generators that have already put into practice cope with this problem by not changing the amount of electric power and operating at around the rated power generation output.
It is surely possible to operate fuel cells at the rated output by presuming the electric power consumption in the case where they are used in the place always having constant electric power consumption such as factories and apartment houses. However, in houses or cars where electric power consumption changes greatly, it is necessary to change quickly the amount of generated electric power by fuel cells according to the electric power consumption.
In view of this, the present invention has an object to provide a electric power generator that can change quickly the amount of power to be generated (fifth object).
The present invention provides an electric power generator equipped with: a hydrogen generator comprising a reformer, a shifter, a purifier, a gas pathway connecting the reformer, the shifter and the purifier, and a generated gas outlet; a polymer electrolyte fuel cell for generating electric power by using a generated gas from the above hydrogen generator and an oxidant gas; a burner for heating at least the reformer; a flow rate controller for controlling a supply amount of a burning fuel to the burner; a communicating pathway connecting the flow rate controller and the burner; a joint where a residual fuel gas exhausted from a fuel electrode of the fuel cell and/or an incompletely generated gas from the hydrogen generator are combined with the burning fuel in the communicating pathway;
said generator being characterized by further comprising a pressure-transferring pipe which transfers a pressure between the joint and the flow rate controller to the flow rate controller, the flow rate controller controlling the supply amount of the burning fuel on the basis of the pressure.
In the above-described electric power generator, it is effective that the flow rate controller comprises a valve, which moves by the pressure between the joint and the flow rate controller.
Also, it is desirable that a switching valve is provided between the joint and the pressure-transferring pipe.
Further, it is effective that the above-mentioned hydrogen generator is equipped with a condensed water outlet.
Moreover, it is effective that the above hydrogen generator is equipped with a condensed water outlet in at least one selected from the group consisting of the reformer, the shifter, the purifier, the gas pathway and the generated gas outlet.
In addition, it is effective that the condensed water outlet is equipped with a switching valve.
Further, the present invention provides a method for operating an electric power generator equipped with: a hydrogen generator comprising a reformer, a shifter, a purifier, a gas pathway connecting the reformer, the shifter and the purifier, and a generated gas outlet; a polymer electrolyte fuel cell for generating electric power by using a generated gas from the hydrogen generator and an oxidant gas; a burner for heating at least the reformer; a flow rate controller for controlling a supply amount of a burning fuel to the burner; a communicating pathway connecting the flow rate controller and the burner; a joint where a residual fuel gas exhausted from a fuel electrode of the fuel cell and/or incompletely generated gas from the hydrogen generator are combined with the burning fuel in the communicating pathway;
said method being characterized by supplying a raw material fuel and water to the reformer when the temperature of the gas pathway between the reformer and the shifter reaches a predetermined lower limit 1 after operating the burner.
Herein, it is effective that the above lower limit 1 is 100xc2x0 C. to 400xc2x0 C.
Also, it is effective that water is supplied between the reformer and the shifter such that the temperature between the reformer and the shifter does not exceed a predetermined upper limit, and that the above upper limit is 250xc2x0 C. to 500xc2x0 C.
Moreover, it is effective to judge that the electric power generator is in the normal operation condition when the temperature at the downstream of the purifier is not lower than a predetermined lower limit 2 and that the lower limit 2 is 100xc2x0 C. to 500xc2x0 C.
Still further, it is effective to control the temperature of the reformer by heating with the burner and to control the temperature of the shifter and the purifier by cooling.
In addition, it is effective to increase or decrease the supply amount of the raw material fuel and water to the reformer after increasing or decreasing the supply amount of the generated gas to the fuel cell according to the increase or decrease of an amount of generated electric power by the fuel cell.